1. Field of the Invention
The present invention relates to a technical field of an oscillation device including an oscillator such as a micro-oscillation member. More specifically, the present invention relates to an oscillation device configured to generate a drive signal for driving an oscillator, an optical deflection apparatus including the oscillation device, and a drive-signal generating method for generating a drive signal in the oscillation device. Examples of such an optical deflection apparatus, which include the oscillation device, include image forming apparatuses such as a projector, a scanning display, an image display apparatus, a printer such as a laser beam printer (LBP), and a digital copier.
2. Description of the Related Art
An existing resonant optical deflection apparatus in which mirrors are driven by resonance is often advantageous over a light-scanning optical system including a rotatable multi-facet mirror such as a polygonal mirror. For example, the size of the optical deflection apparatus can be significantly reduced, power consumption is low, and no facet-to-facet angle mismatch occurs in theory. In particular, an optical deflection apparatus made of Si single crystal, which is manufactured by a semiconductor process, theoretically has no metal fatigue and is excellent in durability (see Japanese Patent Laid-Open No. 57-8520, corresponding to U.S. Pat. No. 4,317,611).
In the resonant optical deflection apparatus, however, in principle, mechanical Q-factor is high so that a deviation between a resonant frequency and a frequency of a drive signal causes a large reduction in drive efficiency, with a consequent reduction in oscillation angle (amplitude) of a deflection mirror. A proposal to address this problem is disclosed in Japanese Patent Laid-Open No. 2005-292627. In this proposal, when a light beam reflected by the deflection mirror is scanned and passes through a predetermined position, a time at which the light beam passes through the predetermined position is detected using a position-detection signal generator including a light-receiving element. A variance table is referred to by a value indicating the number of clocks by which the detected time is deviated from a target time to adjust the drive signal, and the oscillation amplitude and frequency of the deflection mirror are corrected.
U.S. Patent Application Publication No. 2006/0152785 and U.S. Pat. No. 4,859,846 disclose an optical deflection apparatus including two or more oscillators each resonated at either second or third harmonic of a fundamental frequency.